Airborne wind energy system with reduced input torque, better torque handling and optimized speed

Abstract

An airborne wind energy conversion system with lower input torque and/or better handling of the input torque. In one embodiment it has a ground generator, and a tether pulls an elongated member which is meshed with a gear of relatively small diameter. The system achieves relatively high initial RPM and relatively low initial torque. In another embodiment a wide and thin belt unwinds from a spool, having annulus-planet relation with the gear (like in a planetary gearbox). The gear is rotationally coupled to the rotor of the generator. In another aspect, the ratio of the wing air speed to the wind speed is normally below ⅔, which was taught as the optimum since Loyd.

What is claimed is: 
     
         1 . A device for converting wind energy into electrical energy, comprising:
 an airborne member, adapted to harvest wind energy;   a tether, coupled to the airborne member;   an elongated member, coupled to the tether;   a rotational member in contact with the elongated member;   an electrical generator, placed at the ground or water level;   wherein the rotor of the electrical generator is rotationally coupled to the rotational member.   
     
     
         2 . The device of  claim 1 , wherein the airborne member is an airfoil and the device additionally comprises an electronic control system, capable of controlling both the airborne member and the electrical generator. 
     
     
         3 . The device of  claim 2 , wherein the elongated member is non flexible. 
     
     
         4 . The device of  claim 2 , wherein the elongated member is flexible. 
     
     
         5 . The device of  claim 4 , wherein the elongated member is flat. 
     
     
         6 . The device of  claim 4 , wherein the elongated member is a perforated belt. 
     
     
         7 . The device of  claim 4 , wherein the elongated member is a chain. 
     
     
         8 . The device of  claim 4 , wherein the elongated member is relatively straight around its points of contact with the rotational member. 
     
     
         9 . The device of  claim 4 , wherein the rotational member is selected from the group consisting of a sprocket, a gear and a pinion. 
     
     
         10 . The device of  claim 2 , wherein the rotational member and the elongated mesh with each other. 
     
     
         11 . The device of  claim 5 , wherein the elongated member is made of fabric. 
     
     
         12 . The device of  claim 5 , wherein the rotational member is a spool and the elongated member is at least partially wound on the spool. 
     
     
         13 . The device of  claim 12 , further comprising:
 a gear, integrally combined with the spool;   a pinion, meshed with the gear; the pinion being rotationally coupled to the rotor.   
     
     
         14 . The device of  claim 13 , wherein the gear is inside of the spool. 
     
     
         15 . The device of  claim 12 , wherein the spool, and the electrical generator are placed on a rotating platform. 
     
     
         16 . The device of  claim 1 , comprising plurality of elongated members. 
     
     
         17 . A method of converting wind energy into electrical energy, comprising steps of:
 capturing wind energy with a tethered airborne member;   converting motion of the airborne member into periodical linear motion of an elongated member at the ground;   converting the periodical linear motion of the elongated member into rotational motion of the rotational member using frictionless contact;   converting rotational motion of the rotor into electrical energy.   
     
     
         18 . A device for converting wind energy into electrical energy, comprising:
 an airfoil, adapted to harvest wind energy by moving cross wind;   a tether, coupled to the airfoil and to an object on the ground or in the water;   an electronic control system for controlling the airfoil;   wherein the strength of the tether and of the airfoil is optimized for operation with the nominal residual speed coefficient below ⅔.   
     
     
         19 . The device of  claim 18 , wherein the strength of the tether and of the airfoil is optimized for operation with the nominal residual speed coefficient between ⅕ and ½. 
     
     
         20 . The device of  claim 18  further comprising:
 a computing element for setting a low speed threshold below the nominal wind speed and a high speed threshold above the nominal wind speed; 
 a control element for operating the device to convert wind energy into electrical energy when the wind speed is between the low and the high thresholds and to cease the conversion when the wind speed is below the low threshold or above the high threshold.